1. Field of the Invention
The present invention relates to a process and an apparatus for continuously producing elongated bodies changing in elastic modulus longitudinally thereof, such as elongated bodies having an elastic modulus changing stepwise longitudinally thereof, those having a portion with an elastic modulus changing not stepwise but gently, or those having an elastic modulus continuously changing longitudinally thereof.
2. Description of the Prior Art
Elongated bodies of the elastic modulus changing type are suited, for example, for use as catheters which are inserted into the human body or animal bodies for therapeutic or diagnostic purposes. It is required that the catheter be easily insertable into the body, unlikely to damage or injure body tissues and adapted for such torque transmission that when the catheter as inserted in the body is rotated at its base end portion, the forward end thereof is also rotatable with the base end portion. These requirements can be fulfilled if the catheter comprises a flexible forward end portion having appropriate flexibility and elastic modulus, and a base end portion serving as a torque transmitting portion and having rigidity suited to torque transmission. When thus adapted to have varying elastic moduli, elongated bodies of the type mentioned can be used suitably as catheters.
Elongated bodies which change in elastic modulus longitudinally thereof are produced, for example, by a process wherein elongated bodies different in elastic modulus and each having a desired length are joined together end-to-end with adhesive, or fused to each other end-to-end by heating. However, such a method has the drawback that the resulting body becomes altered in outside diameter or reduced in mechanical strength at the joint, and requires much labor for the joining work. Especially when hollow elongated bodies are to be joined to each other, increased difficulty is encountered in joining the bodies without blocking or deforming the hollow channel.
Examined Japanese Patent Publication SHO 54-8036 (1979) discloses a process for producing a "slender plastics tube for medical use," i.e., an extrusion process for continuously producing an elongated body varying in physical properties longitudinally thereof, wherein two kinds of polymer materials which are different in physical properties are alternately fed to a mixing die from respective extruders. Nevertheless, when different polymer materials are merely fed to the mixing die alternately for extrusion as in the disclosed process, there arises the problem that the resulting elongated body varies in outside diameter and in inside diameter longitudinally thereof since the polymers of different physical properties differ in extrusion characteristics and swelling characteristics.